 Hello everyone, welcome to NPTEL Drur Water Resource Management course week 4 lecture 4. In this week we have been focusing on groundwater hydrology and you would have noticed that we are looking at mostly how the groundwater comes into the system, how it gets relocated to different compartments and confined, confined etc. We looked at recharge and how delayed recharge can happen and we also discussed about farmers pumping and how that could actually take more water out than needed if you are not considerate about neighboring farmers. In today's lecture, we would be looking at the types of aquifers based on geology in India. Indian aquifers. So the Indian aquifers as per the government books and reports on groundwater hydrology, you would notice that it is mostly based on the geology. So the major types of Indian aquifers are only two types, the major ones, hard rock aquifers of Peninsular India which represents about 65% of India's overall aquifer surface. If you take 100% as India's aquifer surface, you have the hard rock aquifers as around 65%. Most of them are found in central Peninsular India because that is where you have these hard rock geology. Hard rock as the name suggests, it is a rock which has not been fully disintegrated into soil or unconsolidated materials and minerals. Still there is a lot of consolidated rocks and within the rocks there could be a lot of fractures and that is where the water is stored. And as they clearly say, land is typically underlined by hard rock formation. So the geology, which is the formation, drives the aquifer main and it gives rise to complex, I mean extensive low storage aquifer systems is very, very low in storage. So when you hit hard rock aquifer storage and then you put a pump, it means when you drill in and hit it, what happens is you actually tap into a water which has been there for a millennia or at least 100 years and your understanding is, oh wow, I've taken groundwater now, I've access groundwater, let me take it all, it will recharge but it won't because of the complexity the hard rock aquifers and it is very low in storage. So the storage you see, the volume see, it might be the total volume, it may not recharge. So when you pull all of it out within a year or two, you have depleted your aquifer. Where in the water level tends to drop very rapidly once the water table falls by 2 to 6 meters. So studies have noted that if the water table is lower across the region by 2 to 6 meters, suddenly the water table fluctuates and comes down to very unsustainable levels. Think about the corner of depression, so you have many corner of depressions now and so slowly it is lowering down 2 meters, 3 meters but once it hits around 2 to 6 meters suddenly the water level falls and additionally these aquifers have poor permeability, permeability of letting the water go through the substrate system and that is why it is limited recharge through rainfall. You cannot achieve much rainfall through just rainfall when the author says recharge through rainfall which means natural recharge. You can augment it but still very, very less is going to happen. So this implies the water in these aquifers is non-replenusable and eventually dry out due to continuous usage. So this is the water which is approximately 65% across India and so it is very, very important to preserve this natural resource. And if you do not understand on the availability of the water how the process is happening, people tend to just use it because if they don't use it the next farmer will use it. That mental thing is also there. So if you go to rural regions they will say, sir if I do not use my groundwater someone else will use it. So that concern is also there and that is why we are pushing as a group to convert more into communal groundwater usage wherein everyone is accountable for how much groundwater they use. The second type of major Indian aquifers is aluminal aquifers of the Indo-Gangetic Plains. The author claims that Indo-Gangetic Plains is one of the aquifers but it is overall an alluvial aquifer. What is an alluvial aquifer? The geology is alluvial or just deposited by your rivers and moving water bodies. These aquifers formed in the Ganges and Indus Plains in Northern India have significant storage space because every year you have sedimentations. So once the sediment layer is going thickening every year water can get stored in it and hence a valuable source of freshwater supply. However, due to excessive groundwater extraction and low recharge rates these aquifers are at risk of irreversible over exploitation. So the recharge rates are still low that is the natural recharge rate. When you compare to hard rock aquifers the recharge is much much better and because of the better hydraulic conductivity permeability etc. But the point here to be noticed is that these plains already have good water in terms of surface water the Ganges the Indus these are one of the biggest rivers in the world right. So if you're looking at these rivers and saying that people are still using wrong water which means the demand side has to be managed not the supply side. So if you're having a big river but still you're saying it's not enough and you're going to groundwater so there is some concern of how you use the water. Whereas in northern regions you have these Ganges Indus Plains but when you go to southern regions there's not much big rivers like Cauvery, Krishna all are much much smaller compared to the Ganges. So what would people do in the south if they don't have such a volume? So they are going into groundwater depletion. So that should not be happening in the north regions where you have these Ganges Plains but unfortunately groundwater is being depleted. So there has to be a better understanding of why the water is used. Is it sustainable in the long term or are we just looking at short term benefits? Let's look at the principal aqua systems as given by Central Groundwater Board. They have labeled many in terms of the aqua's and what you could see here is your aqua's are alluvial along the Indus Ganges Plain. Also you would see aqua's alluvial aqua's along the coast where the rivers drain because when the rivers move and drain into the oceans they bring a lot of sediments and sediments become the alluvium material, alluvium aqua. So you would see all these waterways depositing alluvium across and then going into Bangladesh etc. So this is the Brahma Putra bringing in a lot of alluvium, your Brahma your Ganges, your Indus. So all these big big rivers bring in a lot of alluvium and then you have your Krishna and Arun Mada all on the coastal sides you would see Kaveri giving water on the coastal like discharging water into the ocean along the coast but also they would deposit the sediment and form deltas. So those alluvium aqua's are highly rechargeable compared to hard rock aqua's and the central area, central regions were granite mostly granite nieces we call a GNE ISS. So nieces, granites are hard rocks formed from metabolic formations and they do not give in that much groundwater because the spore space is very very limited. It's not the rock opposing, it's not hydrophobic, it is because the spore space is much limited and these rocks are not as weathered as the Himalayan regions. So you would see rocks but it's not as weathered. So what happens is only when weathering happens you have a space for the water to get. So these are also based on the geological survey maps from the Geological Survey of India and we can see a generalized geological map here. So potternary are much much younger geology and those are the sediment driven alluvium, colluvium driven deposits. So you could see a lot of these materials along the river valleys, the big, big river valleys. Whereas the central India is Jurassic, Palestinian volcanic rocks and all the pink color, you will see upper yoke and lower cretaceous continental rocks. So all these are still from the Himalayan regions, you could see off the Himalayas and they are not that much weathered in terms of becoming into porous sediments, porous soil. It is still a hard rock and the hard rock is characterized by fractures. The fractures, first a rock is there, fractures form and then the fractures water and sunlight act upon and then it disintegrates into soil materials. So still there's a lot of hard rock aquifers here which also is a concern that water cannot be stored no longer. So now if you look both of these maps together, you would see that the aquifer mapped aquifer system mapped by the central groundwater board also follows the geology system. So the geology is the key along with that your Indus River and other river basins, Ganges, etc together form these principal aquifer systems of India and it is mostly divided based on the yield, water can be yielded from these aquifers. Now if you see this, you do have a rainfall variable also, it's not only the groundwater, it's not only the rivers but also good. So if you have your Western Guards area, your Ganges regions, you have good rainfall, good storm water in terms of runoff, all these are there. So not much dependency you could see to groundwater but what happens in the central and southern regions where there's much, much lesser rainfall and also not big rivers flowing, you would have to see that most farmers go into groundwater irrigation because they have to do livelihood options for agriculture, domestic urban cities, everyone uses groundwater in the central and southern regions. You saw the geology map which is purely based on the rock material, the rock formations that were much, much deeper formations. So when you say quaternary, Jurassic period, it is not on the top but on the very, very high depth. So that's where also you have some. But when you look at hydrogeological map, it is the hydrology plus the geology map which is made by central groundwater boat, you could see alluvium and confined aquifers, hard rock aquifers along this Indian subcontinent and out of which alluvium and unconfined major aquifer systems contribute to 31% of the area. So the alluvium is here, your blue color and your unconfined which is your top aquifers where unconfined and it is unconsolidated which is mean it's broken formations, those do occupy the light blue and blue colors and it is along the river basins, along the deltas where the river is discharged and it is seen mostly across India in the northern regions and that is close to 31% but the major, major part is your hard rock and semi-consolidated and unconsolidated rocks. So the rock area which is present in the central southern regions are the dominant aquifer type in India. So if you want to map it by yield, the high yielding aquifers are on the alluvium aquifers and on the northern side whereas your central India, southern India is characterized by low yielding formations. You could leave Kashmir and other hilly regions out because most of those regions you don't see much agricultural activities but I'm talking about the central basin and all the other smaller river basins in India where you have so much agricultural activity but very, very less groundwater potential. This knowledge has to be imparted to the farmers because when they put a well they think that oh there's unlimited supply of water but they don't understand that the yield would suddenly stop because everyone starts pumping and as the yield is increasing the recharge if it doesn't increase the water will fall down drastically in water table. So there are multiple studies that have been done to see how these basins, how they recharge on this water and one particular study from Europe showcases that the unconsulted aquifers where you have a little bit more weathered formations. So you could see very high recharge, very high recharge along the ganges and you could see if you visualize further into this figure you could see that high recharge is happening along the river channels, along the major tributaries and that clearly shows that when the gages is flowing it also can recharge and which also relates to again this water machine that we discussed earlier. So there is high recharge approximately greater than 300 millimeters per year. Just think about this number 300 millimeters whereas the rainfall here is only around 600 millimeters, 600, 700 millimeters. So that's a big number just because of groundwater you're getting 300 millimeters of recharge and then you have your high recharge areas. So you have a very high along the ganges, along the tributaries, along the Krishna Pravehi tributary and also you have high recharge, medium recharge all still in the river basins which is you all of your aquifers okay. Then when you come to the complex crystalline aquifers which is mostly found in the central regions, you have a very high recharge in some regions where there's good forest cover, good networks of rivers tributaries and also a lot of rainfall. So do think that recharge can happen only when you have a good material but also you need the rainfall, you cannot have a recharge without rainfall. So that is what this is actually bringing in the hydrological concept also. Then you have the medium recharge in central India and southern India and very low to very, very, very low recharge are less than 20 millimeters per year along pockets and these are the pockets where you have the shadow region of the western guards and you see that the western guards is dark green in color which is very, very high recharge because there's a lot of rainfall, the western guards comes along this angle, there's a lot of rainfall and then it deposits along the western guards Kerala, Maharashtra, Konkan region etc. On the other side of the western guards, Vidarbha and if you come to Tamil Nadu, you would see that there's very, very less rainfall and due to that there's less recharge okay and then there's minor groundwater basins which are also found in Gujarat and these are small groundwater basins formed by unique differences in the geological material. So this image actually clarifies more that you need to understand the geology, you need to understand the hydrology where does the reverse flow, where are the tributaries, where is the deposition happening to understand geological formations and aquifer potential and also the rainfall regions. So the aquifers yield is based on your geology because that is the first one where you can create a port space, the second is the availability of water either through rainfall which is your hydro climate, your rainfall occurring regions, high rainfall occurring regions would have more rainfall to infiltrate and then the third is your hydrology based aquifers wherein along the tributaries, along the tributaries and channels you have a higher yielding aquifers okay. So also if you have a higher yielding aquifers which means more recharge is happening but are they getting into the aquifer too fast? If they do get too fast then there's more interactions between the geological material and that is what you find along the Ganges that there is a lot of natural pollutants in the ground water because there's a lot of arsenic which is a natural pollutant and along the Ganges if you have polluted water coming in and the Yamuna etc because of the high recharge it is not always good because the high recharge rate is there you have to protect the water that goes into these aquifers if you do not maintain the quality it's not only quantity that is important in ground water also quality if you do not maintain the quality then the ground water will be easily polluted in these regions. So now that is a concern for a high recharge area high recharge is good but also if you do not maintain the quality of the water that is going in you are actually polluting the aquifer faster for example let's take a case study if you have polluting agents here let's say industry tannery dying industry for clothes in southern parts and the water is put in the streets the recharge is very low only 20 to 100 millimeters per year so only some pollutants are getting in but if the same goes in the Ganges then think about how much water is recharging the ground water and all this ground water has the potential to bring down the quality of your ground water. So when we do ground water hydrology when we talk about ground water used for rural environments it is as important to talk about the quality as we talk about the quantity because black arsenic, dirt, dead end or polluted water cannot be used for other culture right you don't use salt water in agriculture right so the same way if your ground water is polluted you cannot use so it is as important to maintain the recharge and maintain good quality recharge along with these areas and whenever there's a flood these tributaries do have a backlog of all the flooded water and the flood can actually infiltrate and pollute your aquifers so in Kerala where there's annual level floods every year and Maharashtra Mumbai for example if you do not maintain the flood water and you are sitting in a zone where high recharge is there the flood water once polluted can enter into the ground water aquifer and pollute the entire system unlike your surface hydrology where it's easier to clean the river if it is polluted because for example if a river is polluted people would just let it dry or a big flood can push all the pollutants away but in ground water it's not the case once a ground water recharge occurs it stays there you cannot pull all the pollutants out because the polluting agents might be stuck with the soil and it stays there forever so it is as important to understand the recharge areas and also maintain the water that goes into the recharge areas high recharge areas to get good ground water availability and this is very thinking about the long-term sustainable this is a very very important goal that we should attain to preserve ground water with this I will stop today's lecture let's get into the last next lecture for the wrap-up of groundwater high